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Date: Thu, 23 Aug 2007 22:13:40 +0100
Message-ID: <731EB49F88B309428FFDDD2423F810E403F9E5@HERMES4.ds.leeds.ac.uk>
Thread-Topic: Sticky Meter Pointer 
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From: "Chris Trayner" <C.Trayner@leeds.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
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Subject: LF: RE: Sticky Meter Pointer 
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Hi Steve,

=20
> Any  hints for a pointer than hangs up periodically?

I assume you're satisfied that the problem is with the meter, not the =
circuit sending it a naughty current. I'm also assuming it's a moving =
coil meter.

Three suggestions. Apologies if you're already thought of them, and if =
they're teaching grandmother to suck eggs.

1. Needle bent, scraping on the plastic/glass or on the scale.=20
Cure: dismantle meter and bend pointer gently back.

2. Bearings either too tight or (possibly) too slack.=20
Cure: dismantle and examine the bearings at each end, the ones the =
rectangular coil pivots in. With posh meters, you sometimes find that =
one of these can be adjusted by screwing it in or out. Patience may be =
needed to find the best setting. There may be a lock nut.

3. Grit (especially metal filings) in the works. This can get between =
the moving coil and the pole-pieces it rotates within.
Cure: (you've guessed it) dismantle and clean out.=20
If the muck is magnetic (e.g. iron/steel), try to wipe it along the =
magnet away from the poles and towards the middle(ish) of the magnet, =
where you have some chance of pulling the bits off. This can be an =
extremely finicky and aggravating job.
If the muck is non-magnetic, I suppose just brush or blow it out - I've =
never been lucky enough to have non-magnetic muck ;-(

Two big words of warning:

Meters are v-e-r-y delicate, especially the coil springs that return the =
pointer to zero. The reason I now dismantle them with confidence (though =
also a sinking feeling) is that I wrecked a couple in my teens, and =
learnt the hard way.

I've given myself frequent problems dismantling meters on my workbench - =
in fact, doing so has probably been the main reason for having to clean =
them!
The problem is that my workbench has plenty of bits of steel and iron =
lying around: filings from things I've made/sawn/filed/etc. over the =
years. Dismantled meters are a very good way of cleaning it up! The muck =
jumps to the strong magnets of a meter with evident glee. I would =
suggest dismantling the meter somewhere else, e.g. on a dining room =
table.


Good luck!
Chris G4OKW


-----------------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032


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